* Joerg Roedel <joerg.roedel@amd.com> wrote:
> + /*> + * * This may be no bug in reality - but most implementations of the> + * * DMA API don't handle this properly, so check for it here> + * */
You must be using Vim and copy & paste messed up? :)
Ingo
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On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote:
> > * Joerg Roedel <joerg.roedel@amd.com> wrote:> > > +#define err_printk(dev, format, arg...) do { \> > + error_count += 1; \> > + if (show_all_errors || show_num_errors > 0) { \> > + WARN(1, "%s %s: " format, \> > + dev_driver_string(dev), \> > + dev_name(dev) , ## arg); \> > + } \> > + if (!show_all_errors && show_num_errors > 0) \> > + show_num_errors -= 1; \> > Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket > so if two errors hit at once on two CPUs then the error tracking variables > can be accessed at once.> > I'd suggest a simple global lock for this error case (taken inside the > hash bucket lock), to be on the safe side.> > Also, please dont use a macro for this - printk details can be passed in > to helper inlines/functions too.
Yeah, this is not SMP-safe, I know. But debugfs does not support
atomic_t so I made the variables u32. But at least a race condition has
not a too bad impact. What may habben is that error_count misses a error
or the show_num_errors become negative.
But if we really want to avoid this I think its better to add atomic_t
support to debugfs. What do you think?
Joerg
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On Sun, Jan 11, 2009 at 08:57:52AM +0100, Joerg Roedel wrote:
> On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote:> > > > * Joerg Roedel <joerg.roedel@amd.com> wrote:> > > > > +#define err_printk(dev, format, arg...) do { \> > > + error_count += 1; \> > > + if (show_all_errors || show_num_errors > 0) { \> > > + WARN(1, "%s %s: " format, \> > > + dev_driver_string(dev), \> > > + dev_name(dev) , ## arg); \> > > + } \> > > + if (!show_all_errors && show_num_errors > 0) \> > > + show_num_errors -= 1; \> > > > Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket > > so if two errors hit at once on two CPUs then the error tracking variables > > can be accessed at once.> > > > I'd suggest a simple global lock for this error case (taken inside the > > hash bucket lock), to be on the safe side.> > > > Also, please dont use a macro for this - printk details can be passed in > > to helper inlines/functions too.> > Yeah, this is not SMP-safe, I know. But debugfs does not support> atomic_t so I made the variables u32. But at least a race condition has> not a too bad impact. What may habben is that error_count misses a error> or the show_num_errors become negative.> But if we really want to avoid this I think its better to add atomic_t> support to debugfs. What do you think?
Even a global lock will not really help here because show_num_errors and
show_all_errors can be set using debugfs. Either we live with the small
race (with limited impact) or I add atomic_t support to debugfs.
Joerg
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On Sun, Jan 11, 2009 at 12:11:27AM +0100, Ingo Molnar wrote:
> > * Joerg Roedel <joerg.roedel@amd.com> wrote:> > > +#define err_printk(dev, format, arg...) do { \> > + error_count += 1; \> > + if (show_all_errors || show_num_errors > 0) { \> > + WARN(1, "%s %s: " format, \> > + dev_driver_string(dev), \> > + dev_name(dev) , ## arg); \> > + } \> > + if (!show_all_errors && show_num_errors > 0) \> > + show_num_errors -= 1; \> > Note that the arithmetics here is SMP-unsafe: we only hold the hash bucket > so if two errors hit at once on two CPUs then the error tracking variables > can be accessed at once.> > I'd suggest a simple global lock for this error case (taken inside the > hash bucket lock), to be on the safe side.
As I wrote in a previous email, a race here is no big deal. I add a
comment to document it. Or do we want another global lock here?
> Also, please dont use a macro for this - printk details can be passed in > to helper inlines/functions too.
Hmm, how does this look like? There is not WARN variant which can use
va_args as a parameter. And it is important that the error message is
logged in the warning itself. So the driver developer can see it when a
user reports the warning.
Joerg